1. Field of the Invention
The present invention relates generally to hard disk drive seeking and, more particularly, to a method, apparatus and computer program for improving the seek performance of a sinusoidal seek servo.
2. Description of the Related Art
Hard disk drives include a plurality of magnetic transducers that can write and read information by magnetizing and sensing the magnetic field of rotating disks. The information is typically formatted into a plurality of sectors that are located within annular tracks, which are located across the surface of the disk. A number of vertically similar tracks are often referred to as a cylinder. Each track may therefore be identified by a cylinder number.
Each transducer is typically integrated into a slider that is incorporated into a head gimbal assembly (hereinafter xe2x80x9cHGAxe2x80x9d). Each HGA is attached to an actuator arm. The actuator arm has a voice coil located adjacent to a magnet assembly which together define a voice coil motor. The hard disk drive typically includes a driver circuit and a controller that provide current to excite the voice coil motor. The excited voice coil motor rotates the actuator arm and moves the transducers across the surfaces of the disk(s).
When writing or reading information, the hard disk drive may perform a seek routine to move transducers from one cylinder (or track) to another cylinder. During the seek routine the voice coil motor is excited with a current to move the transducers to the new cylinder location on the disk surfaces. The controller also performs a servo routine to insure that the transducer moves to the correct cylinder location.
Many disk drives utilize a xe2x80x9cbang-bangxe2x80x9d control loop for the servo routine to insure that the transducer is moved to the correct location. The shape of the current waveform for seek routines that utilize bang-bang control theory is typically square. Unfortunately, square waveforms contain high frequency harmonics which stimulate mechanical resonance in the HGA causing acoustic noise. This acoustic noise tends to increase settling time. Thus, while the bang-bang control method may provide the best theoretical seek performance, the accompanying settling characteristics result in a less than optimal overall seek time.
The recent use of sinusoidal waveform algorithms for seek trajectories was aimed at improving the settling time by decreasing the acoustic noise exhibited by the bang-bang control method. In particular, seek trajectories based on sinusoidal algorithms exhibit superior acoustic noise properties, thereby reducing the settling time. However, sinusoidal waveforms for seek trajectories do exhibit some degradation in seek performance for shorter seek lengths as compared to the bang-bang control method. While, the overall degradation of seek performance for sinusoidal seek algorithms is somewhat compensated by the decreased acoustic noise of a sinusoidal seek trajectory, there is still a performance gap between sinusoidal seek trajectories and bang-bang seek trajectories for shorter seek lengths.
Thus, there is a need for a method, apparatus and computer program which further reduces the performance gap between the sinusoidal seek algorithm and the bang-bang seen algorithm, while not sacrificing the improved settling characteristics of the sinusoidal seek algorithm.
The present invention comprises a method, apparatus and computer program for performing a servo seek according to a voltage-constrained sinusoidal acceleration trajectory. In one embodiment, the method comprises exciting a voice coil motor that is coupled to the transducer so that the transducer performs a seek having a seek length and a seek time, said transducer to move across the disk surface with an essentially sinusoidal acceleration trajectory. In addition, the seek is to be performed using a substantially constant voltage applied to the voice coil motor over one or more seek lengths. In another embodiment, the substantially constant voltage applied to the voice coil motor is in range of between 10 and 12 volts.
Other embodiments are described and claimed herein.